Although hair is known to be removed by laser light by using a hair growth modulation device using light as described in Japanese Patent Application Laid-open No. 2001-292285, attention is currently being focused on modulation of the growth of body hair with light having a quantity of light or luminous energy that does not cause changes in cell morphology as observed with existing therapeutic lasers.
Although body hair has a hair cycle during which hair changes in cycles consisting of a growth period, a regressive period and a rest period, when light, having a quantity of light or luminous energy that does not cause changes in cell morphology as observed with existing therapeutic lasers, is irradiated during the above-mentioned rest period, together with growth of hair during the growth period of the hair cycle proceeding rapidly, the absence of the occurrence of cell damage as well as the absence of the occurrence of adverse side effects such as burns has also been confirmed. In addition, when hair is irradiated with light of the above-mentioned quantity of light or luminous energy during the growth period of the hair cycle, hair growth has been confirmed to be effectively inhibited.
Furthermore, although the reason why scalp hair growth is promoted or inhibited when the hair is irradiated with light at a level that does not cause changes in cell morphology during the rest period or growth period is not clear, based on the results of analyses at the RNA level, activation of inflammatory cytokines is thought to occur as a result of the light irradiation, and the resulting promotion or inhibition of hair growth is thought to be the result of this activation of inflammatory cytokines.
However, in promoting or inhibiting hair growth by irradiating light for modulating hair growth as described above to human skin, it is only required to radiate light of a suitable light quantity without having luminous energy in the manner of a laser in order to modulate hair growth, and for this reason a xenon flash lamp is used for the light source. However, if it were possible to lower the required quantity of light even further, optical modulation of hair growth is expected to become more appealing since it would be possible to use other light sources that are inexpensive and easy to use.